The purpose of this study is to determine the maximum tolerated dose, within 30 to 90 mcg, of interferon beta-l1 in subjects with relapsing and secondary progressive MS who have moderate to severe disability. In addition, the study will research the best additive treatment regimen, if any, that achieves the maximum tolerated dose (MTD). Safety data will also be obtained for use of 30 to 90 mcg of interferon beta-1a. Finally measurements of the principle proteins that participate in the inflammatory and regulatory processes will be conducted.